Easy open end of a metal-plastic construction

ABSTRACT

An easy open end for food and beverage cans having reduced aluminum content is provided in an end having a metal polymer metal laminate construction. An opening panel as defined in the end body by a pair of first and second spaced apart score lines disposed in the first and second major surfaces, respectively. Each of the first and second score lines define an area of reduced thickness for both the metal layer and the adjacent polymer layer. The opening panel can be displaced from the remainder of the end body to provide an easy opening can by perforating the end body at a point along the first and second score lines.

BACKGROUND OF THE INVENTION

The invention belongs to the technical area of the application oflayered metal-plastic material construction to packaging and moreprecisely to the fabrication of easy open ends used for closingcontainers containing food or beverage products.

More precisely still, the metal-plastic construction applied is of thetype metal-polymer-metal, that is in which a foil of polymer issurrounded by two metal foils to which it is adhered.

In the text of the present patent application, we will use, withoutdistinction for these constructions, the terms metal-plastic-metal,metal-polymer-metal, or more simply in an abbreviated fashion, MPM.

1. Problem Posed

Easy-open ends for food or beverage cans are generally constituted of ametal foil covered on the inside of the can by a protective varnishavoiding contact of the foods or of the beverage with the metal of theend and preserving the cover from corrosion and the contents fromcontaminations.

These easy open ends possess a system of perforation and a tearing line.The system of perforation is constituted most frequently by a ringconnected to a punch. When one pulls on the ring to move it from aposition parallel to the end to a position perpendicular to the end, thepunch perforates the cover at a place located on the line of weaknesscorresponding to which the tearing continues when one continues to pullon the ring. The line of weakness or of tearing can have various designsaccording to whether one wishes to achieve an opening in the form of apour panel (the case of the beverage can) or a full panel opening of thecan (the case of food cans).

In both cases, the line of weakness or tearing is obtained by scoringthe outside or the inside face of the end. It is not unusual in fact,notably for steel food can ends to score the internal face and laterrepair the damaged internal varnish layer. This method presents twoadvantages: the first is that it is easier to achieve in this manner thebalance between ease of opening and the resistance to accidentalopening; the second is that even with an outside score, the deformationof the metal induces small cracks in the internal varnish. But thesesmall cracks are practically impossible to repair whereas the largernotches resulting from the internal scoring can be easily repaired byelectrophoresis. The weakening in both cases is caused by the smallerquantity of metal present under the base of the score, as this is shownin cross-section in FIG. 1 where (1) designates the metal, (2) theexternal incision, and (3) the layer of inside varnish.

The problem posed initially to the inventors was that of improving thebeverage can. Of a capacity in general of 33 centiliters, of acylindrical shape, this can is closed by an easy open end, coatedinternally by a food approved varnish and externally by one or severallayers of decoration indicating the nature and the brand of thecontents. These coatings are in general applied after the forming of thecan.

Among the elements of cost of the beverage can, the cost of the metal,despite its slight weight, constitutes a preponderant portion. The ideahad therefore occurred to the researchers of replacing a part of themetal by a less costly material: plastic.

The inventors have found a solution to this problem consisting of ametal-plastic construction composed on a foil of thermoplastic polymercoated on each of its faces with a metal foil with an intermediateadhesive layer. They have then asked themselves if such a metal-plasticconstruction would not also be able to replace the metal sheet used forthe preparation of the ends. Aside from the economic advantages, thissolution would facilitate the recycling of the ends which would be madestarting from a product identical to or similar to that of themetal-plastic cans of a similar type of MPM structure.

But even with the conventional easy open ends having a thin protectiveorganic coating, it is difficult to arrive at an acceptable balance ofeasy opening and the protection against an accidental opening duringtransportation and storage. If the scoring of the metal is not deepenough, the opening is too difficult, if it is too deep, the resistanceto accidental opening is insufficient.

The achievement of this balance is particularly difficult because thedifference in residual thickness between an end which opens too easilyand an end which opens too difficultly is so slight that the normaltolerances of the tooling or their normal wear can perturb the desiredbalance.

This demand for precision of the residual thickness of metal is stillmore difficult to satisfy if one tries to score an MPM end with knowntooling for traditional ends. If one scores the outside of the end, itis necessary that the score completely penetrate the outside metal layerand make a notch in the internal layer deep enough to create stressconcentrations sufficient for tearing the metal. As each metal layer issignificantly thinner than with a conventional end, the balance betweenthe ease of opening and the resistance to accidental opening is stillmore difficult to attain.

The simultaneous or successive scoring of both metal layers from theoutside and inside at the same location does not completely resolve theproblem of leaving a determined thickness of residual metal in the metallayers.

Some attempts have been made to avoid this need for precision of theresidual thickness in the case of all-metal ends by using two scoreswhich are laterally displaced in the plane of the end. Because of thehigh strength of the alloys used in metal ends, these scores must bespaced with only a small lateral distance between scores. Not only doesthis still require a high degree of precision, but there is a danger ofcracks propagating from one score to the other very proximate scoreduring the scoring process or during shipment and handling.

With paperboard covers for other types of containers, such double scoreshave been more successful. This success can be attributed to the eastwith which paper tears. This ease of tearing allows the scores to beplaced farther apart.

On the contrary, plastics are notoriously difficult to tear because oftheir ability to undergo plastic deformation rather than to propagate acrack or a tear.

Even when a very thin film of plastic is adhered to a thick metal foil,the plastic does not tear cleanly. For example, when the interiorvarnish of conventional metal ends is replaced by a plastic film, thelatter deforms to a great extent at the moment of tearing, generating afault designated as "feathering." This feathering is a result of plasticdeformation and is characterized in that the cut across the plastic,instead of being clean and straight, is irregular and stretched such asshown in FIGS. 2a and 2b. FIG. 2a represents the score line in the metal(5) and the layer of plastic material (6) before tearing. FIG. 2brepresents with the same numerical designation the three elements aftertearing. One sees the tapered or feathered shape of the tear in theplastic material.

Since the preferred plastic thickness in a metal-plastic-metal can endis several times that of a plastic film which serves only to protect ametal can end from corrosion, the tear resistance of plastic would beexpected to be even more of a problem for metal-plastic-metal ends.

2. Description of the Prior Art

The French patent application, published Mar. 13, 1992, under U.S. Pat.No. 2,666,564 in the name of GIE Pechiney Recherche, brings a solutionto the problem of feathering when a plastic film replaces the varnish ona conventional metal end. This solution consists of an easy open can endof a metal foil and plastic film which encompasses, in addition to themechanical score of the outside face of the metal foil, a continuousdepression of the plastic film on the inside at the line of themechanical scoring. This continuous depression is obtained by aconcentrated source of heat, for example a laser beam.

However, this solution would not be applicable to the metal-plasticconstructions developed in the present invention since the layer ofplastic material is sandwiched between two metal foils.

Single scores in metal can ends are well known in the prior art. Forexample, U.S. Pat. No. 3,990,376 (J. R. Schubert) describes a singlescore end in which the resulting sharp edge of the removed panel isprotected by folded metal in such a way that the protecting folded metaldoes not interfere with the opening of the end.

Double scores which are laterally displaced have also been described inNL-A-8900863 (assigned to Hoogovens Groep), in U.S. Pat. No. 4,126,244(W. F. Elser) and in U.S. Pat. No. 4,129,085 (G. B. Klein). NL-A-8900863states that the residual metal thickness between the two score amountsto 20 percent of the original end thickness. U.S. Pat. No. 4,126,244also describes two very proximate scores in stating that in order toreliably provide a predefined, selectively weaker path of fracture inthe wall section, the interspacial distance between the channels shouldbe substantially less than the basic average thickness of the wallsection. Although U.S. Pat. No. 4,129,085 does not state a particularlateral distance between the scores, the drawings show them to be veryclose, in fact overlapping, to such an extent that only a thin sectionof metal is left between the two scores. The scores are described asbeing so close that if the two scores are made sequentially, metal willbe pushed into the first score when the second score is subsequentlycut.

In U.S. Pat. No. 4,564,119 (assigned to Nippon Light Metal KK), theinventors show two scores which are laterally more distant from eachother in an all-metal end. In this case, one of the scores is anauxiliary having the score residual greater than that of the severingscore in order to afford an appropriate deformation of the can end.Since this auxiliary score is designed not to fracture, this inventionfalls within the general area of single score ends in terms of theactual mode of fracture.

Double score paperboard covers for other types of packages have beendescribed in U.S. Pat. No. 3,185,578 (E. W. Scharre) and FR-A-1279093(F. C. Mennen). U.S. Pat. No. 3,185,578 in particular shows a paperboardcover in which one portion of the cover can be removed before anotherportion in order to provide selective heating of different types offood. The paperboard of the cover is preferably coated on both sides bymoisture resistant materials, one of which may advantageously bealuminum foil. Paperboard being easy to tear, the purpose of the offsetscores which penetrate through the moisture barrier layers is to preventwicking of moisture through the cover and to preclude penetration offoreign matter into the container. FR-A-1279093 describes a popcorncontainer consisting of an aluminum tray, an expandable aluminum foilcover, and a rigid paperboard cover which protects the expandable foilcover. In at least one of the embodiments of this invention, the tearingof the paperboard cover is controlled by a double score.

The PCT application WO91/18795, published Dec. 12, 1991 in the name ofAmerican National Can Company, describes an easy opening means appliedto the wall of a plastic container consisting of notching the inside andoutside faces of the wall and creating a zone of weakness in theinterior of this wall. As indicated by FIG. 1A of that application, theoutside face encompasses two notches situated at different heights ofthe container and the inside face, one notch, situated at anintermediate height.

That application however, appears to be far removed from the presentinvention: first, it does not involve ends but the upper part of thewall of a container; furthermore, it involves plastic containers and notmetal-plastic; finally, it uses three notches, two exterior and oneinterior and the part of the walls included between the two exteriornotches is detached from the container at the moment of opening.

None of the above prior art describes a double scoredmetal-plastic-metal end with its peculiar problem of propagating a tearthrough a tear resistant plastic core.

Metal-plastic-metal structures per se are described in EP-A-0019835 (DowChemical Company), EP-A-0046444 (Schweizerische Aluminum), EP-A-0034781(BASF Aktiengesellschaft), WO-A-8200020 (Metal Box Limited), andEP-A-0115103 (Sumitomo Chemical Company). These patents describemetal-plastic-metal sheets, processes for making these sheets, orprocesses for converting the sheets into various articles. None of theseinventions describes ends, whether easy open or standard, nor any othertype of rupture or tearing of such structures.

3. Object of the Invention

The invention has for object an easy open end fabricated from ametal-plastic construction of the type metal-plastic-metal, or inabbreviated form MPM, of which the line of weakness or of tearing isaccomplished in a particular manner: it involves two scores made in themetal foils of the construction and satisfying particular geometricconditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents in cross section a tear line of the prior art on endsvarnished interiorly.

FIGS. 2a and 2b represent the mode of tearing of a simple metal-plasticconstruction with one layer of metal and one layer of plastic.

FIG. 3a represents in cross section a metal plastic MPM constructionutilized in the invention.

FIG. 3b represents in cross section a tear line according to theinvention.

FIGS. 4a and 4b represent a beverage can end in which the opening paneldisplaces only in the direction toward the interior of the can andremains attached to the end after opening.

FIGS. 5a and 5b represent an end of a food can in which the openingpanel is first pushed toward the interior of the can at the moment ofthe initial perforation, then detached by pulling toward the exterior ofthe can.

DETAILED DESCRIPTION OF THE INVENTION

The invention concerns an easy open end provided with a tear line in ametal-plastic construction of the type metal-polymer-metal intended forthe closing of food or beverage cans characterized in that the tear lineis formed of two neighboring scores in which one is in the metal foil onthe outside of the end, the other in the metal foil on the inside of theend.

The invention is illustrated in FIGS. 3a and 3b. FIG. 3a represents incross section the metal-plastic construction used in the development ofthe invention. This construction includes a central layer ofthermoplastic polymer (7) on each face of which is adhered a metal foil(9). A thin layer of adhesive can be interposed between polymer andmetal.

FIG. 3b represents a cross section in a plane perpendicular to thedouble scoring, after realization of this double scoring by theclassical technique of stamping. The polymer and the metal are stilldesignated by the marking (7) and (9) while for reasons of clarity ofthe drawing, the adhesive layer is not shown. The scores in the metalfoils are designated by (10) and (11). One observes on the drawing that,at the score line, not only the thickness of the metal but also that ofthe plastic has been reduced.

Despite the relatively high initial thickness of the plastic and thefact that the score itself does not penetrate into the plastic core, theend of this invention opens easily and cleanly. This is particularlysurprising given the previously described problem with feathering with amuch thinner layer of plastic adhering to a single layer of metal.Although this clean tearing might be partially attributed to thesurprising decrease in plastic thickness directly under the score, therelative thickness of this residual plastic is still greater than thatof the plastic film with which feathering was observed.

Although the explanation for this enhanced tearing is not completelyunderstood, it is apparently related to the fact that the plastic istrapped between two relatively rigid metal layers. When a free film of amaterial such as a plastic is stretched in one direction, its plasticdeformation in that direction is accompanied by a contraction in theother planar direction and by a reduction in its thickness. Because theplastic core layer in the metal-plastic-metal end of this invention isrestricted by the two metal layers from contracting in these twodirections, it acts like a stronger but stiffer material. This addedstiffness apparently concentrates the stress discontinuities within theplastic which are generated by the rupturing of the metal score to alarge enough extent to overcome the added strength; thereby resulting ina clean and easy tear.

Even if there remains a thickness of residual metal in the two metalliclayers, the force required for opening is not determined only by thisthickness of the residual metal. This force depends jointly on thethickness of the residual metal, on the distance between the twoincisions, or else on the shear strength of the plastic core, or else onthe shear strength of the adhesive between the plastic core and eachmetal layer, or else on the adherence of the adhesive on each metallayer. But, the distance between the two scores is much easier tocontrol and to maintain constant than the thickness of the residualmetal because it is significantly greater than the thickness of theresidual metal and, therefore, less sensitive to normal tolerance oftool wear. It is also less sensitive to wear, first because it islarger, but also because its direction is perpendicular to that of thetool displacement and, therefore, to the variation of dimensionresulting from the repeated impact of this tool.

If the thickness of the residual metal is slight, the opening force willbe determined essentially by the easy to control distance between thetwo incisions and to a lesser degree by the residual metal. In fact,even if one of the layers was completely sheared, a balance between theresistance to the accidental opening and ease of opening can be found.

Furthermore, the inventors have found that the thickness of residualmetal was not as sensitive to slight variations in the tooling as in thecase of an entirely metal end in reason of the capacity of the plasticto undergo deformation in the zone of the incision.

The geometry of this double incision should preferable meet certaincriteria depending on the thickness of the metal of that of the plastic.If one calls;

e_(m) the metal thickness

e_(p) the plastic thickness

p the depth of incision

d the distance between the center lines of the scores

l the width of the score at its exterior dimension,

the following relationships should preferably be respected:

    2e.sub.m 3<p<e.sub.m +e.sub.p,

    100 μm<d<1000 μm, and

    P/2<1<2p.

The relative positioning of the incisions on the inner side of the endand on the outer side should be adapted according to the type of end.

A first relative positioning, FIG. 4, corresponds to beverage can endsin which the opening panel is displaced in a single direction towardsthe interior of the can and remains attached to the end after opening.FIG. 4a shows the opening panel as seen from above. In this mode ofrealization, the periphery of the external score (10) ought to beentirely interior to that of the internal score (11) in a fashion thatthe panel can completely span the orifice. FIG. 4b shows an interruptedcut of the end, and of the opening panel along aa' with two externalscores (10a) and (10a') and two internal scores (11a) and (11a'). Therupture occurs at the points marked (12) and it is clear that thecentral panel can easily span the opening.

Another application of this first positioning is a conventional endopening with a can opener which exerts a vertical downward shear forcesuccessively on all the perimeters of the end.

A second positioning, FIG. 5, corresponds to ends, for example foodcans, in which the opening panel if first pushed towards the inside ofthe can at the moment of the initial perforation, then detached bypulling towards the outside of the can. FIG. 5a shows the opening panelviewed from above. In this method of realization, the periphery of theexternal score (10) should be interior to that of the internal score(11) in that part near to the perforation, then exterior, aside fromthis part. The two score lines, interior and exterior, cross of eachother at two points (14) and (15). The rivet (16) serves to attached thering. FIG. 5b represents an interrupted cut of the end and of theopening panel along aa' with the two external scores (10a) and (10a')and the two internal scores (11a) and (11a').

A third positioning according to the invention is that of an end inwhich the opening panel is displaced in a single direction towards theexterior of the can and detaches itself completely from the cover afteropening. In this mode of realization, the perimeter of the externalscore ought to be completely exterior to that of the internal score.Although such a panel externally lifted had been at one time the normfor beverage can ends, it has still been difficult to achieve for fullpanel opening ends for food cans by reason of the large force forinitiating the tearing of the score. But with this invention, however,the initial opening force can be easily controlled by the method of deepscoring of the two metal layers combined with a reduction of thedistance between the two scores in the region of the end where openingcommences.

Aside from the economic advantages and an improved adjustment of theopening force, the invention presents other advantages. The first isthat the corrosion on one or even both metal layers to the point ofperforation does not involve leaking or contamination of the product byoutside organisms. In the case where both metal layers would beperforated, there could, of course, occur passage of gas between theproduct and the external environment, since the plastic core is not anabsolute barrier to the gas. As the area of these perforations is small,the passage of gas will be also very small. In addition, the path of gaspassage across the plastic will be very long, at least unless theperforations in the two metal layers are exactly one above the other.But, as most perforations occur along the score lines and as, accordingto the invention, these lines re staggered, the passage of gas will bevery slight.

In addition, with such MPM ends, one can choose the alloys to limitcorrosion. For example, the alloy used for the internal layer can bechosen to minimize corrosion in the presence of a particular food andthe alloy chosen for the outside layer can be chosen for its mechanicalstrength or its resistance to corrosion in contact with a givenenvironment.

Another advantage of the invention appears in the case of ends forpressurized products such as gaseous beverages. This advantage lies inthe fact that the force exerted when one opens the container is directedfrom the outside to the inside, whereas the principal force foraccidental opening is directed from the inside towards the outside. Thepositioning of the score in the internal layer laterally to the exteriorof the score in the external layer furnishes a supplementary protectionagainst accidental opening provoked by the internal pressure, since itis impossible for the internal layer to pass through the smaller openingin the external layer.

A common problem with can ends is to prevent the sharp edges of theremoved cover and of the metal resting on the can from causing wounds.This problem is perhaps even more acute with MPM ends. The shear of theplastic core could, in effect, occur in two different fashions:

(a) If the shear resistance of the interface is less than the internalshear resistance of the plastic, one observes a delamination of the corefrom one of the metal layers. This thin unglued metal layer thenpresents an edge particularly sharp. In this case, the can can bedesigned in a fashion to protect this sharp edge by an adjacent part ofthe can. An example of such protection consists in that the wall of thecan body presents a shape such that the opening is above a shoulder ofthe can, preventing the user's fingers from coming in contact with thesharp residual metal. With such a model, the shear should occur adjacentto the protected edge in a fashion that the other edge (for example, theedge of the removed panel) be protected by the full thickness of theplastic core. This selective rupture of the adhesion can be accomplishedsimply by the utilization of a less adherent adhesive on the surfacewhere one wishes that the tear occur.

(b) If the shear resistance of the interface is greater than theinternal shear strength of the plastic, one then observes a shear withinthe plastic core which leaves the edges coated with a relatively thicklayer of plastic and thus prevent wounds.

To direct this shear, either to the interface with the metal or towithin the plastic core, one utilizes a layer of polymer of weakcohesion in which the rupture propagates. This layer can be one of theadhesive layers, the polymer core proper, or a supplementary layer whichcan be situated, for example, with the plastic core. The advantage ofusing such a layer rests in the fact that the rupture can be controlledby the mastery of the cohesion of the material used. The choice of thematerial of weak cohesion should be, of course, made as a function ofits compatibility with the other materials used in the structure. It isknown that the addition of non-reinforcing fillers to the polymer allowsa reduction of mechanical properties and, in particular, its propertiesof resisting rupture, therefore of diminishing its cohesion. Theconcentration of the non-reinforcing filler assures the control of thecohesion of the material in question.

Fillers presenting clivage planes only slightly adherent in the same wayas some minerals, such as mica, can thus diminish the cohesion ofpolymers.

Another possibility consists in using two layers of polymers of weakcompatibility of the sort where the rupture occurs at the interfacebetween the two layers. The two layers can be coextruded or applied withthe usual techniques of induction. The degree of compatibility betweenthe two materials used permits the mastery of the adhesive rupture whichoccurs upon the opening of the end.

Preferably, the metal-plastic construction presents certaincharacteristics of thickness and of composition.

The thickness of the different constituents of the construction willadvantageously conform to the following specifications: (in microns)

    ______________________________________                                               Metal         25 to 100                                                       Adhesive      0 to 10                                                         Polymer       80 to 300                                                       Adhesive      0 to 10                                                         Metal         25 to 100                                                ______________________________________                                    

In that which concerns the composition of the constituents:

The polymer constituting the cores is chosen among one of the followingthermoplastic polymers: polypropylene, high and low densitypolyethylene, polyesters, polyamides. It is interesting to note that,the polymer not being in contact with the food product or beveragecontained in the container, it is possible to use recycled polymers.Trials have been made on the recycled polyester and polypropylenes andgive completely satisfactory results.

The adhesive, preferably interposed between the polymer and the metal,is either a thermosetting polymer, for example of the type polyurethaneor epoxy, or a thermoplastic polymer, such as polyolefins modified inthe classical fashion by a ethylenic acid (maleic, crotonic, etc.),ethylene-acrylic polymers, polyesters, or different copolymers of themonomers corresponding to the polymers indicated above.

The metal is either of steel, tin plated or not, coated with chrome,with zinc, with nickel, or with chrome-chrome oxide, of aluminum or analloy of aluminum. An aluminum alloy, preferably in a hardened state, ispreferably used.

The metal-plastic construction objects of the invention are prepared bydifferent known methods. The most commonly used are direct co-extrusion,heat sealing, and induction gluing. These last two methods arepreferably practiced on a continuous line fed with plastic films andmetal strips.

Direct co-extrusion consists of extruding between the two metal foilswhich unroll continuously and which constitute the external layers, thecentral polymer layer and on one side and the other of this centrallayer the two thin layers of adhesive. The composite product thusobtained passes then between the rollers in order to achieve theadherence between the different layers. This technique evidently appliesjust in the case of thermoplastic adhesives.

Heat sealing consists in starting with a composite strip of polymersincluding a central layer of polymer coated on each of its faces by theadhesive layer, here also thermoplastic, and of introducing this stripbetween two metal foils. The heat bonding is assured by the passage ofthe composite product thus obtained between two rolls heated to atemperature sufficient to melt or at least soften sufficiently theadhesive layer in a fashion to guarantee the adhesion between thepolymer core and the metal foils.

Finally, the gluing by induction consists of coating the inside faces ofthe two metal foils with a thermosetting adhesive by a known method andof applying these foils from one side and the other or the strip ofcentral polymer with the aid of rollers.

The fabrication of the ends according to the invention is done bydrawing in utilizing the usual techniques. The two score lines can bemade simultaneously or successively.

The ends which are the object of the invention can be attached to alltypes of cans, beverage cans, food cans, by all types of means ofattachment: seaming, gluing, heat sealing.

EXAMPLES Example 1:

A strip of polypropylene of 140 microns in thickness has been coated oneach of its faces with a layer 5 microns thick of adhesive constitutedby a film of maleic acid modified polypropylene. The two films ofadhesive have been applied on the polypropylene film by cold passagebetween the rolls. The composite strip thus obtained has then beencontinuously introduced between two foils of 80 micron thick of aluminumalloy 3003, a manganese alloy according to the "Aluminum Association"standards, each unwound starting from a bobbin and preheated by passagein an oven at a temperature of 200° C. in a fashion to melt theadhesive. The MPM composition obtained was then passed between rollsexerting a pressure around 400 kP_(a), then rolled onto a bobbin.Starting from this construction, circular discs of 75.4 mm diameter werecut. These discs have then been drawn for giving ends of 65 mm andprovided with an external tear line (shown as solid line) and aninternal tear line (shown as dotted line) forming the shape representedin FIG. 4. These ends have then undergone an examination which has notevidenced any cracks in the metal or the plastic. No delaminationbetween the metal and the plastic has been observed. In addition, thetearing of the scored lines was achieved in a perfect fashion withoutthe phenomenon of feathering.

Example 2:

A layer of low density polyethylene of 150 microns in thickness has beenextruded between two foils of 80 microns thickness of aluminum, eachunwound from a bobbin and preheated by passage in an oven at atemperature of 200° C. without interposition of adhesive. The MPMconstruction obtained was then passed between rollers exerting apressure around 4000 kP_(a), then rolled onto a bobbin. Starting fromthis construction, circular discs 94 mm in diameter were cut. Thesediscs have been then drawn to give ends of 81 mm in diameter andprovided with an external tear line (shown in solid line) and aninternal tear line (shown in dotted line) assuming the shape representedin FIG. 4. These ends have then undergone the same examination as thoseof Example 1 and resulted in the same observations.

We claim:
 1. An easy open can end comprising:a drawn end body having agenerally circular configuration including a first major surface adaptedto be inwardly facing and an opposed second major surface adapted to beoutwardly facing when the can end is joined to a can body, said end bodyhaving an M_(i) -P-M_(e) type laminar construction wherein M_(i) andM_(e) are inner and outer metal foil layers, respectively, each metalfoil layer having a thickness of from about 25 to about 100 microns, andP is a central polymer layer, having a thickness of from about 80 toabout 300 microns, said end body further including an opening paneldefined by a first score line disposed in said first major surface, anda second score line disposed in said second major surface, wherein thefirst score line defines an area of reduced thickness for the metallayer M_(i) and polymer layer P and the second score line defines anarea of reduced thickness for the metal layer M_(e) and the polymerlayer P, and wherein the centerline spacing, d, between the first scoreline and the second score line is greater than about 100 μm, saidopening panel being movable to define an opening in said end body byperforating the end body at a point along said first and second scorelines and, thereafter, tearing the end body along the first and secondscore lines by displacing at least a portion of the opening panel from aremainder of said end body to define said opening.
 2. An easy open canend as defined in claim 1, wherein the centerline spacing, d, betweenthe first score line and the second score line is from about 100 μm toabout 1000 μm.
 3. An easy open can end as defined in claim 1, whereinsaid first and second score lines each have a configuration including adepth dimension, p, and a width dimension, l, taken at an outer facingsurface of the respective metal layer such that2/3 e_(m) <p<e_(m)+e_(p), wherein e_(m) is the metal layer thickness and e_(p) is thepolymer layer thickness; and 1/2 p<l<2p.
 4. An easy open can end asdefined in claim 1, wherein said metal foil layers M_(i) and M_(e) areselected from the group consisting of aluminum, aluminum alloys, steel,tin-plated steel and chrome coated steel.
 5. An easy open can end asdefined in claim 1, wherein said polymer layer P is selected from thegroup consisting of polypropylene, low density polyethylene, highdensity polyethylene, polyester and polyamide.
 6. An easy open can endas defined in claim 1, further comprising an adhesive layer in saidlaminate disposed between said polymer layer P and each of the metalfoil layers M_(i) and M_(e).
 7. An easy open can end as defined in claim6, wherein said adhesive layers have a thickness of up to about 10 μm.8. An easy open can end as defined in claim 1, wherein metal foil layersM_(i) and M_(e) are of the same material.
 9. An easy open can end asdefined in claim 1, wherein metal foil layers M_(i) and M_(e) are ofdifferent materials.
 10. An easy open can end as defined in claim 1,wherein the shear strength of polymer layer P is less than the shearstrength of each M_(i) -P and M_(e) -P interface such that on opening,tearing occurs within polymer layer P.
 11. An easy open can end asdefined in claim 1, wherein the shear strength of polymer layer P isgreater than the shear strength of each M_(i) -P and M_(e) P interface,such that on opening, tearing occurs at the M_(i) -P and M_(e) -Pinterfaces.
 12. An easy open can end as defined in claim 1, whereinpolymer layer P is a unitary polymer layer.
 13. An easy open can end asdefined in claim 1, wherein said polymer layer P comprises anon-reinforcing filler.
 14. An easy open can end as defined in claim 1,wherein said polymer layer P comprises a plurality of polymer layers.15. An easy open can end as defined in claim 14, wherein polymer layer Pcomprises two different polymer layers of low compatibility.
 16. An easyopen can end as defined in claim 14, wherein one of said polymer layersin P has low cohesion to reduce the shear strength of polymer layer Pand facilitate tearing.
 17. An easy open can end as defined in claim 1,wherein said first and second score lines each have a generally 3-sidedwedge-shaped configuration.
 18. An easy open can end as defined in claim1, wherein said first score line is disposed inwardly from said secondscore line.
 19. An easy open end can as defined in claim 1, wherein saidfirst score line is disposed outwardly from said second score line. 20.An easy open can end as defined in claim 1, wherein a first portion ofsaid second score line is disposed inwardly from said first score lineand a second portion of said second score line is disposed outwardlyfrom said first score line.
 21. An easy open can end as defined in claim1, further comprising means connected to said opening panel tofacilitate perforation and displacement of the opening panel to definesaid opening.
 22. An easy open can end as defined in claim 1, whereinthe distance, d, between the centerlines of the first and second scorelines is reduced at a point where perforation upon opening is intendedto occur.